The present invention relates to clamping, holding and releasably fastening workpieces, particularly workpieces of a thin configuration, but having large surfaces areas; more particularly, the present invention relates to holding such workpieces by means of low pressure suction.
U.S. Pat. No. 3,771,082 describes a system for holding, fastening and clamping workpieces under utilization of a relatively large machine tool table which is provided for holding and supporting individual fastening elements of various configurations and various constructions, whereby, in particular, in some instances certain features are provided for utilizing low pressure suction in one form or another including the suction of workpieces themselves. FIG. 25 of the patent discloses a particular mounting element which by and in itself is to be fastened on the machine tool table mentioned above and which is provided with a universally pivotable carrier permitting various angular orientations of a particular mounting surface and permitting also the application of a low pressure to the surface of the workpiece at which it is held and supported by that pivotable head. A particular holding element of this type is not necessarily used for fastening the workpiece per se, but for providing supplemental support and for preventing the workpiece from vibrating during working.
It can also be said that the present invention relates to improvements in the pivotable support of large area workpieces within a system as disclosed in said patent and practicing the best mode of the present invention can be understood to occur within a system of the general scope as per the above mentioned patent.
Workpieces of particular interest are, for example, thin metal sheets, such as they are used as skin covering for aircraft. Some of these sheets are, for example, manufactured and shaped to have a spherical or other well-defined curvature. This curvature must not be distorted so that it is required during further working of such a curved sheet to support it strictly commensurate with that shape and without deforming or distorting it generally or locally. In the past this problem has been solved by placing the workpiece onto a correspondingly shaped templet or the like and to fasten the workpiece in surface to surface engagement to that particular holder under utilization of suction and/or mechanical fastening elements. It it apparent that the particular templet is, of course, of very limited use; it serves as a holding element for one type of workpiece only, any workpiece having a different curvature or being larger will not be adequately supported and protected by such a templet. One must consider that in many instances a large variety of curvatures, curves and contured parts exists. Therefore, it is quite apparent that the amount of tooling needed is quite extensive; the reservoir of templets is substantial. This, of course, is in addition to the requirement that each of these templets must be very accurately manufactured in the first place.